Continuous heating transformation diagram and austenitic grain refinement in a commercial brazilian boron steel

Although conventional heat treatment methods have been widely employed for decades, their limitations have become increasingly evident, particularly regarding energy inefficiency, high operational costs, and emissions associated with long heating and cooling cycles.In this context, fast-heating techniques such as Ultra-Fast Heating (UFH) have emerged as promising alternatives by combining sustainability, high productivity, and the potential for microstructural refinement, which can lead to superior mechanical properties in steels.This study aimed to determine the Continuous Heating Transformation (CHT) diagram and to evaluate the effect of heating rate on the austenitic grain size (AGS) of a commercial Brazilian boron steel.Dilatometric tests were performed under different heating rates to determine the critical austenitizing temperatures (Ac 1 and Ac 3 ) and to construct the corresponding CHT diagram.Additionally, microstructural analyses were carried out to reveal and quantify the AGS for each condition.The results showed that increasing the heating rate shifts the critical transformation temperatures to higher values, highlighting the kinetic effects on phase transformations.Moreover, higher heating rates promoted significant grain refinement, reducing the average grain size from approximately 60 μm to about 10 μm solely through thermal control.These findings demonstrate the potential of UFH as an effective tool for microstructural engineering, enabling the optimization of mechanical properties while improving the energy efficiency of industrial heat treatment processes.